Implantable cardiac rhythm management devices, including pacemakers and implantable cardioverter/defibrillators (ICDs), are devices used to treat abnormalities of heart rhythm. Pacemakers, for example, treat bradycardia (i.e., a heart rate that is too slow) by delivering pacing pulses to the heart at appropriate times, while ICDs terminate fibrillation by delivering a defibrillation shock pulse to the heart. Such devices containing pulse generating circuitry for delivering pacing or shock pulses that is enclosed by a housing and connected by leads to electrodes disposed in or near the heart. Many cardiac rhythm management devices incorporate both ICD and pacemaker functionality in the same device.
Most cardiac rhythm management devices use a capacitive discharge circuit to deliver either pacing or shock pulses to the heart. Owing to their high energy density and ability to withstand high voltages, electrolytic capacitors are used in these devices. An electrolytic capacitor is a layered structure that includes a metal anode plate with an insulating oxide layer formed on its surface for constituting a dielectric, a metal cathode plate, and an electrolyte impregnated in a separator between the two plates. The metal used for the anode and cathode plates is usually aluminum or tantalum. A capacitor is thereby formed from the capacitance between the negatively charged electrolyte and the positively charged anode plate with the oxide layer acting as a dielectric. A stacked-type electrolytic capacitor generally includes a stack of flat capacitive elements, with each element including a paper separator between two sheets of aluminum, one serving as an anode plate and the other as a cathode plate. In a stacked-type of aluminum electrolytic capacitor, anode and cathode plates (also referred to as coupons) are cut from aluminum sheets in a shape designed to conform to a capacitor case. The capacitive elements are connected together in parallel to provide a total capacitance.